128 Gregory — Progress in Interpretation of Land Forms. 



found its place as a major geologic agent and has given 

 a new conception of natural scenery. Lofty mountains 

 are no longer "ancient as the sun," they are youthful 

 features in process of dissection; valleys and canyons 

 are the work of streams and glaciers; fiords are erosion 

 forms; waterfalls and lakes are features in process of 

 elimination; many plains and plateaus owe their form 

 and position to long-continued denudation. Modern 

 landscapes are no longer viewed as original features or 

 the product of a single agent acting at a particular time, 

 but as ephemeral forms which owe their present appear- 

 ance to their age and the particular forces at work upon 

 them as well as to their original structure. 



It is interesting to note the halting steps leading to the 

 present viewpoint, to find that decades elapsed between 

 the formulation of a theory or the recording of signifi- 

 cant facts and their final acceptance or rejection, and to 

 realize that the organization of principles and observa- 

 tions into a science of physiography has been the work 

 of the present generation. Progress has been condi- 

 tioned by a number of factors besides the intellectual 

 ability of individual workers. 



The influence of locality is plainly seen. Convincing 

 evidence of river erosion was obtained in central France, 

 the Pacific Islands, and the Colorado Plateau — regions 

 in which other causes were easily eliminated. Sculpture 

 by glaciers passed beyond the theoretical stage when the 

 simple forms of the Sierras and New Zealand Alps were 

 described. The origin of loess was first discerned in a 

 region where glacial phenomena did not obscure the 

 vision. The complexity of the Glacial period asserted by 

 geologists of the Middle West was denied by eastern 

 students. The work of waves on the English coast 

 impressed British geologists to such an extent that plains, 

 of denudation and inland valleys were ascribed to 

 ocean work. 



In the establishment of principles, the friendly inter- 

 change of ideas has yielded large returns. Many of the 

 fundamental conceptions of earth sculpture have come 

 from groups of men so situated as to facilitate criticism. 

 It is impossible, even if desirable, to award individual 

 credit to Venetz, Charpentier, and Agassiz in the formu- 

 lation of the glacial theory; and the close association of 

 Agassiz and Dana in New England and of Chamberlin 



